How can I fade in and out between cameras during animation?
What Todd says does work, but it is not the best way of doing things.
Go to the Video Editing Screen Layout. Add a Scene strip, and then add the same Scene strip again so you have the two scenes on top of each other. In the properties panel (key N with the cursor inside the VSE portion of your screen), go to the Scene part and to the Camera Override. Select one camera in the first Scene strip, and the second camera in the second Scene strip. The `Scene strips will now have the added text of the names of the cameras along their length.
Next, add a Cam Multicam Effect Strip. Make sure it is directly on top of the two Scene strips. Click the 1 button to select the camera notated by the bottom Scene strip, or 2 to select the camera notated by the top Scene strip. Then move your cursor to where you want the fade to begin  and select 1 or 2, whichever you didn't select the first time. It will cut the strip into two parts.
Now move the first half of the Cam Multicam strip up to channel 4. Drag the right arrow of the top Cam Multicam strip to the frame where you want the fade to end.
Select the first strip, and then the second strip, and then key Shift +A and add a Gamma Cross Effect Strip. Your finished setup should look like this and provide the same result as Todd's.

Further research: Multicam selector documentation.